The objectives of reactive chemical and nonreactive thermal processing with laser radiation are outlined giving indication that processing with laser radiation is governed by a hierarchy of time constants originating from photon-matter interaction, phase transition dynamics, laser source excitation fluctuations, and optical feedback in combination with the influence of beam delivery systems, processing/shielding gas flow configurations, robotics, production lines and environment. The minimization of losses by heat flow, reflection and transmission and the stringent need for quality assurance require as first approach the control of processing, which is mainly due to the capability of laser radiation source. The current status of laser radiation sources is reported giving information on the state of the art of processing with laser radiation in combination with subsequent demonstration of future trends and developments with respect to radiation sources, beam delivery, beam shaping, materials, processing and quality assurance.

Recently, ETCA has bought an industrial high power CO2 laser of 22 kW from United Technologies Industrial Lasers. Before its use in material processing, a beam characterisation is necessary. We describe the set-up used to measure the power level and its fluctuations, the beam intensity profile at the near field and the far field and the polarization state of the beam. After a brief description of the laser, some measurement results are given.

With the increasing use of high-power lasers, especially CO2 lasers, in the field of industrial laser-materials processing numerous applications occur, in which diagnostics of laser-beam characteristics may help to maintain or to increase processing quality and reproducibility as well as system reliability. Three different types of diagnostic devices are presented, developed to monitor the total laser power, the intensity distribution of unfocused as well as focused beams, and the beam position. The practical use of these systems is discussed with some examples typical for the industrial applications of high-power-lasers.

we present the results of a systematic evaluation of the main optical characteristics of our lasers. The tests were performed on a 3 kW and a 5 kW model, and included measurements of the near field, the far field and the focussing quality. The radii of curvature of the mirrors were chosen to form a stable resonator. The gain coefficient and saturation intensity were determined using the Rigrod-analysis. In the recent literature, RF-excited CO2-lasers are considered to behave superior in terms of plasma properties. In this paper, we analyse and concentrate on the optical proper-ties of our DC-excited lasers. The beam quality was measured using a rotating wire type of beam analyser. Quality factors between 80 and 95% of the diffraction limit were measured at levels between two and four kilowatt. This means that the lasers are capable of emitting the lowest order transverse mode up to the highest industrially available power levels, using DC-excitation.

Diffraction from structured surfaces is discussed as a new principle in high power laser beam optics. Useful properties of structured surfaces include, for example, polarization anisotropy, diffractive beam splitting and diffractive attenuation. Since these surfaces can be fabricated from low-loss materials, e.g. metals, the intrinsic absorption can be low enough to allow operating power levels high in the multikilowatt range. Several practical devices for high power laser beam handling can be based on diffractive concepts. For example, linear and circular polarizers can be fabricated as all-metal mirrors. These can be used both intra-and extracavity, and can be integrated into focusing surfaces. Diffractive loss from all-metal perforated screens has already been used to develop a precision step attenuator with applications in beam diagnostics as well as in laser process studies.

Many applications of ultraviolet (UV) lasers would be greatly facilitated if the designers and users of associated optical systems could characterize the beams as to location, size, shape and intensity distribution at selected points along the optical path. We describe a new technique based upon visible light fluorescence induced into a crystalline plate when irradiated by a UV beam as a means for performing these measurements. Instruments applying this principle and allowing the user to observe the otherwise invisible beam as well as to quantify its intensity profiles using electronic and/or computer analysis methods also are described.

Laser technology, once considered a solution looking for a problem, is becoming more and more popular in industry and in particular in the field of material processing. The laser is used in many different application areas as a powerful tool well suited for welding, cutting, drilling, heat treating and so on.

Since only a short time thin fiber cable, which can transmit high laser power, i.e. more than one kilowatt cw power, are on the market. To have a thin and at the same time powerful fiber has special advantages for material processing. It used to be a big problem to transfer laser radiation from the laser source over a long distance to the work piece. For material processing such as cutting or welding reproducable beam conditions at the focus point are necessary. By using mirrors for beam transportation, it is very normal that the stability at the focus point depends very much on the mechanical stability of the mirrors and on other factors influencing beam propagation. To avoid part of these problems sometimes the laser head was mounted on 1 or 2 axis of xy table, see fig. 1. A lot of work has been invested in the past years to optimize mirror systems for CO2 lasers, when sheet metal of larce format bad to be cut.

In material processing as well as in medicine a number of fiber applications for laser power transmission are being widely used. Power transmission via fiber is generally ex-pected to be of increasing importance in future developments. As in all advanced techniques high performance of a laser fiber system is desired, e.g. - high transmission efficiency - high power density attainable after the light having been passed through the fiber - high safety standards and - high flexibility of the fiber cable.

During the pst fifteen years, pwerful lasers have been developed for industrial applications such as cutting, piercing, welding, engraving, etc... Convenient and reliable delivery systems are still needed to widen their field of application.

A lot of industrial Nd:YAG lasers are now being equipped with fiber optics for application in flexible manufacturing. One laser can be supplied with several fibers so different processing positions can receive laser power according to the time-and/or energy sharing principle. Most of the time-sharing devices (multiplexers) are based on a galvanometer mirror that couples a converging laser beam into different fibers respectively. From the industry several questions have risen to make these multiplexers faster, more reliable and suitable for smaller diameter fibers. The current designs are limited by the positioning accuracy of the galvanometer mirror and by their sensitiveness to variations in the parameters of the laser beam due to thermal lensing effects. In the patented design of the multiplexer presented here, based on a telescopic image relay and a precision fiber positioning unit, these problems were solved. A prototype has been built which addresses five fibers with 200 μm cores at a switching rate higher than 100 times per second. The fibers have special termination connectors and can be exchanged easily without losing the alignment of the optical system. For spot welding applications with pulsed Nd:YAG lasers this means that this type of multiplexer could be used to take advantage of the high laser pulse rates and the pulse shape and energy programming possibilities that manufacturers of these types of lasers offer nowadays. Another application that has been shown now is the use of several remote laser engraving units served by a single CW/Q-Switched Nd:YAG laser and a fiber multiplexer.

A comprehensive approach to delivering the beam of a multi-kilowatt industrial laser is described throughout its entire path length from laser exit to beam impingement on the part. The importance of sharing the beam among workcells to fully utilize the laser is emphasized. Attention to each aspect of beam handling in providing rapid, reliable, and safe delivery of the beam can help ensure the success of laser processing in production.

Special requirements are needed for highly flexible, multi station laser processing. Linkage of several lasers with various handling stations causes different kinds of tasks to be solved in the fields of optics, electro mechanics, laser technology and opto electro-nics. A new design for flexible high power CO2 laser beam handling has been developed, including self-checking security systems, laser beam diagnostics, easily adjustable high power beam bending mirrors, high precision motorized mechanics and computer controlled user guidance.

For a continuous high quality laser cut, it is necessary among other things to position the focal point of the laser beam correctly. This means that a constant clearance between the cutting head and the workpiece with a tolerance of +/- 0.Imm must he ensured. When cutting corrugated automobile bodysheet for example, a good quality cut can only be achieved with automatic clearance control. In the following, a method of automatic clearance control is described using the assistance of a noncontact capacitive sensor system. The copper nozzle of the laser cutting head acts as the electrode of the clearance sensor. The nozzle electrode and the workpiece build a small variable capacitance depending on the clearance. A change of clearance also changes the capacitance, which in turn influences a high frequency oscillator circuit. This shift in frequency is then converted into an analogue DC signal, which can be used to operate a servo motor control for the positioning of the laser cutting head in a closed loop servo system. Laser cutting heads with clearance sensor nozzles of different shapes, suited fur most applications in the industry, with focal lengths from 2.5" to 5" have been developed. They are capable to cut metal sheet from 0.2 to 12 mm of thickness, using CO2-lasers with output power up to 2.5 kW. For special applications involving difficult workpiece topographies in automobile production applications special "trunk" nozzles have been developed. For 5-axis cutting machines and robots, new laser cutting heads with integrated nozzle sensors in combination with a high dynamic Z-axis motor drive are in a stage of development.

The research and development programs in manufacturing science at The Pennsylvania State University have a major emphasis on laser materials processing technology development. A major thrust of this program is the development of an intelligent robotic system which can manipulate a laser beam in three dimension with the precision required for welding. The robot is called LARS for Laser Articulated Robotic System. A gantry based robot was selected as the foundation for LARS and the system is divided into five major subsystems: robot, electronic control, vision, workhead, beam transport, and software. An overview of the Laser Robotics program including laser materials processing research programs will be provided.

The focused laser power beam is a thermal tool able to make clean cuts of metallic structures without introducing stresses in the workpiece. The amount of drosses produced is much smaller than for another tool. These properties are interesting to use the laser tool in hostile environments encounte-red in nuclear dismantling operations. In this specific application, it is necessary to take into account the constraints of the nuclear environment : radiations, confinment, aerosol products ; as also the technolo-gical laser constraints : transportation of the laser beam, crossing of the hot-cell wall, cutting of 3D structures. The first constraint is this of a remote work. We have been lead to develop a specific tool. This tool consists in five axis arm, slim enough to be introduced in a 10 inches diameter hole. The total length is 1.70 m, therefore the slenderness is very high compared with the weight (22 Kg). In this paper we present the technical elements of this laser robot : mechanical structures, articulations, actuators, beam handling system, nozzle cutting head and the robot controller. We give the first results obtained with this tool on different kind of workpieces in a non-active environment. This work is a cooperative programm with the Commission of the European Community (ROLD project).

The advantages of laser technology for remote machining in hot cell are well known. In this paper are reported the results of an experimental work carried out to determine the attenuation of r radiation by a copper mirror in order to design the optical systems to deliver a high pow er CO2 laser beam into a hot cell. Moreover a system to control the workpiece position with respect to the high power laser beam focal point is described.

The performance of high power laser systems depends strongly on achievable beam quality, which determines focus intensity on the work-piece at given laser power. To minimize wavefront aberration limiting the beam quality, active optics are a very promising tool. A survey of active optics systems and technology is given with special attention to high power lasers. Sources and properties of beam distortions typical of high power lasers are described. Various basic concepts for measuring and correcting optical aberrations in real time are discussed. Related instrumentation is described, in particular wavefront correction devices like adaptive mirrors and wavefront sensors. Examples of active mirrors for a high-power CO2-laser system and their technical features are presented. Finally, performance and limitations of active optics systems in high power laser systems are discussed.

For most laser hardening industrial applications, CO2 laser with power in the range 1-10 kW are used. To obtain the proper hardened path and thickness it is usually necessary to set up an optical system to guarantee the required beam energy distribution on the component. Beam shaping techniques using static and moving optical components will be discussed evaluating their reliability for an industrial environment. Two examples of beam shaping system are described; both employed with a stationary component and a computer controlled path. The first optical system uses a three mirror rotating homogenizer to heat treat cylinder bores of about 100 mm. The second system includes a light pipe integrated at the end of a laser robot cartesian system to heat treat large 3 dimensional components.

The recently developed cauability to diamond turn ZnSe, has led to a number of useful optical components for high power CO2 lasers which were not previously available on a cost effective basis. For example, aspheric lenses can provide tighter focused spots; axicons can convert solid beams to donut shaped beams and vice-versa, or can be used as beam integrators; multifaceted prisms and pyramids can easily divide a beam into several parallel beams. This paper will explain the working principles of these diamond-turned optics and give examples of material processing applications.

A method is proposed to eliminate the central hole present in the annular beams emitted by lasers equipped with unstable resonators. The method is based on the use of conical reflectors, or axicons. The first axicon is converging with a 45° cone angle; the second axicon is diverging with a 45° cone angle. The converging axicon has a central hole of diameter equal to the diameter of the diverging axicon. It can be shown that the combination of these two axicons yields an output laser beam with a near field of hyperbolic shape and a far field where 89% of power is contained in the central lobe. Inadequate axial positioning of the axicons or inappropriate values of the cone angles result in a degradation of the optical quality of the far field; the tolerance to such errors is evaluated for typical CO2 laser parameters.

Reflective metallic optics for high power CO2 laser are very important in industrial application of laser surface modification processes (cladding, heat treatment, etc.). Copper wirrors fabricated by diamond turning method offer a very high reflectance in the IR spectral region. Usually, metallic mirrors are coated with protective films to preserve the surface from any kind of degradation. In the development of these optics, we have produced a system for heat treatment. Such a system uses a beam integrator convex mirror that divides the CO2 beam laser in several beams with a predetermined spot size. By a concave mirror all spots are overlapped on the surface which must be treated. In this way, it is possible to obtain a uniform intensity, distribution of radiation on the irradiated surface. Using different beam integrator convex mirrors, various spot sizes at the same focal distance can be achieved.

Multifaceted mirrors for providing uniform intensity of the laser beam over a well-defined area are a valid alternative to kaleidoscopes and scanning optics in laser surface treatment applications. Beam integrators usually provide intensity distribution uniformity of higher quality but their applications are limited since they are less flexible than kaleidoscopes and scanning optics. Optical reimaging systems increase their flexibility but nevertheless they are still difficult to handle automatically due to the large number of degrees of freedom to be controlled. New arrangements of reimaging systems are currently being studied at RTM and the results are discussed in this paper. Initially a converging beam integrator was applied with a single spherical mirror used as a reimaging system. Flexibility was achieved by manually adjusting the position of the spherical mirror. A more complex reimaging system, based on several mirrors, was designed and assembled. The performances of both systems were tested in laser surface treatment applications with laser powers of up to 15 kW. Diverging beam integrators were considered on account of their low cost and wider availability in Italy. Reimaging of these beam integrators presents different problems and offers new possibilities. Reimaging systems with automatic handling of the mirrors were designed by RTM researchers The problems and advantages of these automatic and flexible beam integrating systems are discussed in detail.

Using a stable-unstable resonator, formed by cylindrical mirrors, a homogeneous, rectangular intensity distribution can be generated directly by a high power CO2 -laser oscillator. Such a beam shape is especially well suited for wide area heat treatment applications. The advantages of such a resonator and the focussing properties of the resulting beam will be discussed in detail. Examples of applications, demonstrating these advantages will be given.

The definition of the Gaussian Principal planes is presented based upon the conventional criterion of conjugate planes with lateral magnification equal to 1. These Principal planes split and move depending on the gaussian width of the incoming beam and the focal length of the system. The object-image relation using the frontal distances referred to the Gaussian Principal planes becomes, in the classical approximation, to the usual formula of the lens. Graphical techniques are used to find the Gaussian Principal planes in a simple way. The use of these planes allows us to analyze resonators and to design optical systems in which the beam is in variant.

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Advanced PhotonicsJournal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews